Man arrested for 2x4 labeled "High Powered Rifle"
It is a punishment, for the reason that "yesterday" you could buy it, but today you can't, and the reason for that change occurring was that the day before yesterday Larry had one in his pants pocket when he committed a crime. So we unwind the chain: Larry committed a crime. He had this "widget" in his pocket. Congressman says, "Oooh, Larry bad! We must remove all widgets!" Now Bob can't buy the widget.
So yes, literally Bob is punished for Larry's crime. That's uncool.
I thought about the speed limit analogy myself a long time ago. It doesn't quite fit, because there is some speed beyond which it is unsafe to drive, period. Likewise, it is never ever safe to drive a car while drunk. We could spend an hour or two deciding upon the arbitrary cut-off points for both speed and blood-alcohol level, but the point is that there is a limit beyond which nobody can safely drive around other people. You can't say the same about clip size. Clips of 5, 10, 30, 50, and 100 all operate identically all the time.